Workpiece cloth positioning is typically carried out prior to a sewing operation by positioning a workpiece cloth relative to a sewing needle so that the sewing needle strikes through the intended start point of the subsequent stitches being formed. When the sewing machine is standing by for execution of a sewing operation, a needle bar to which the sewing needle is attached generally assumes an elevated position where the tip of the sewing needle is lifted away from the workpiece cloth. Such arrangement is obviously unsuitable for precise workpiece cloth positioning, and thus, the user was required go through a troublesome task of lowering the needle bar to proximate the tip of the sewing needle to the upper surface of the workpiece cloth as much as possible through the user's manual rotation of a pulley.
One possible solution to such inconvenience is proposed in a sewing machine disclosed in JP S62-207492 A, in which the sewing needle is lowered from the elevated position by the user's depression of a switch until it is stopped at a preset position immediately before contacting the workpiece cloth. The above configuration allows smooth and error-free workpiece cloth positioning in starting off the sewing operation on the workpiece cloth (establishing the first needle drop).
In positioning the workpiece cloth relative to the sewing needle, the user is allowed to move the workpiece freely by keeping a presser foot elevated. However when there is absolutely no constraint in the movement of the workpiece cloth, the user is required to provide some extent of manual pressure to prevent displacement of the workpiece cloth. In other words, the workpiece cloth being unlimited in its movement will subject itself to frequent displacement, which in turn renders workpiece cloth adjustment more troublesome for the user.
Further, since a feed dog protruding and retracting from a needle plate for feeding the workpiece cloth is moved in synchronism with the vertical movement of the needle bar, the feed dog is unwontedly elevated above the needle plate when the sewing needle is stopped at a position above the needle plate. Thus, during workpiece positioning, smooth workpiece cloth transfer may not be possible depending upon the material of the workpiece cloth if the material is prone to be seized by the elevated feed dog.